1. Field of Invention
The present invention relates to a field of medical prosthesis manufacture, and more particularly to an adjustable complex of an artificial cervical vertebra and an intervertebral connector.
2. Description of Related Arts
Because of the population aging, increasing proportion of desk workers as well as computer users, high traffic accident rate and other factors, patients with cervical vertebra problems such as cervical spondylosis, cervical vertebra fracture and cervical vertebra tumor are increasing. Emphases of surgeries for patients with cervical vertebra problems, especially with cervical spondylosis and cervical vertebra fracture due to the cervical intervertebral disc herniation, are put on: a) reducing pressing, wherein the factors pressing the spinal cord and the nerve root should be eliminated in such a manner that nerve functions can recover faster after the surgery; and b) stabilizing, wherein different types of fusion surgeries are provided and different implant materials (such as autograft bone, allograft bone and artificial vertebra) are utilized for long-term postoperative stabilization. Among the surgeries, the anterior intervertebral disc nucleus pulposus excise with subtotal corpectomy for decompression and intervertebral fusion is currently the most important surgery, and is the surgery with the greatest application advantage. The benefits comprise simple decompression, thorough discectomy and high fusion rate. Anterior intervertebral fusion comprises autograft bone, allograft bone and artificial vertebra grafting fusion. Autograft bone graft has significant osteoinductive, osteoconductive and osteogenesis. Therefore, the surgery has become a gold standard for bone grafting fusion. Advantages of autograft bone grafting fusion are no immunogenicity and fast fusion. However, shortcomings thereof are high postoperative loss rate and secondary damage of harvested bone area (such as donor site bleeding, fracture and infection). The allograft bone graft avoids the above disadvantages, but immunogenicity exists and fusion speed is slow (often takes six months or even more than nine months).
In order to overcome the above disadvantages of autograft and allograft bone graft, postoperative substitute has been looked for. As a result, artificial vertebra was invented. In 1969, Hamdi first reported vertebral tumor excision of patients with waist 2 plasma cell tumor and metastatic adenocarcinoma, and replaced the pathological vertebra with prosthesis (Hamdi, F A. Prosthesis for an excised lumbar vertebra: a preliminary report. Can Med Assoc J, 1969, 100, 12: 576-80.). According to the materials, the artificial vertebra can be classified into artificial vertebra made by metal materials, artificial vertebra made by new composite materials and artificial vertebra made by other materials. According to the structure and function, the artificial vertebra can be classified into pure supporting type, bracing and fixing type and adjustable fixing type. The pure supporting type artificial vertebra is mainly mounted on an upper vertebra and a lower vertebra by injecting bone cement for filling the bone defeat caused by vertebra excision. The fixing effect thereof is poor. The bracing and fixing type artificial vertebra is mainly mounted on an upper vertebra and a lower vertebra by spikes for instantly stabilizing the vertebra. Titanium mesh is the most commonly used artificial vertebra for bracing and fixing and is widely used in the reconstruction of the vertebra. However, length of the titanium mesh is fixed and is nonadjustable. Therefore, the choice of the vertebra is very strict, otherwise it is difficult to restore the ideal vertebral height. Besides, risk of falling exists. Different adjustable fixing type artificial vertebras with a variety of characteristics have been developed by scholars in the world. And the artificial vertebras have achieved a certain effect in clinical application. For example, the Synex artificial vertebra has a titanium hollowed mesh structure and a length thereof is adjustable. Knop and other people utilized the Synex artificial vertebra for the reconstruction of the anterior injury of thoracic and lumbar vertebra for providing sufficient 3-dimensional stability of the vertebra. However, after length adjustment, posterior implant of the Synex artificial vertebra is difficult and technical requirement is high. Therefore, the anterior or combined posteroanterior surgery has a serious trauma and takes a long time (Knop, Christian; Lange, Uta; Reinhold, Maximilian; Blauth, Michael. Vertebral body replacement with Synex in combined posteroanterior surgery for treatment of thoracolumbar injuries. Oper Orthop Traumatol. 2005, 17 (3): 249-80.). Zhao Dinglin (Zhaoding Lin, Chen De, Zhao Jie, et al. Research and clinical applications of adjustable hollowed artificial vertebra. Chinese Journal of Orthopaedics, 2001, 21:222-224.) has developed a hollowed adjustable titanium alloy artificial vertebra. A length thereof is adjustable for ideally recovering vertebral height. Because of a hollowed structure, bone graft is able to be provided therein in such a manner that prosthesis is permanently fused with the vertebra. However, only spikes contact with the upper and lower vertebras for mounting and the prosthesis is rigidly mounted. Therefore, the internal bone graft has problems of stress shielding and bone resorption.
The shapes and materials of the artificial vertebras are adjusted and improved for simplifying the surgical steps, reducing surgical trauma, realizing instant postoperative stabilization, and fastening fusion. However, the above artificial vertebras have the same problem that the operated vertebras will completely lose original movability after the surgery, which is considered to accelerate postoperative cervical degenerative disease, lead to cervical intervertebral disc herniation of the adjacent vertebras, and cause vertebral bone hyperplasia, etc. Long-term follow-up results illustrated that after the anterior cervical vertebra fusion surgery, up to 92% of patients had adjacent segment degeneration, although the clinical symptoms are not consistent with the severity of the X line (Goffin, Jan, Geusens, Eric, Vantomme, Nicolaas, et al. Long-term follow-up after interbody fusion of the cervical spine. J Spinal Disord Tech, 2004, 17(2): 79-85.). Hilibrand and the others found that after anterior fusion surgery, clinical symptoms related to adjacent segment degeneration occur to about 2.9% of patients each year. Furthermore, the statistical results illustrate that clinical symptoms caused by adjacent segment degeneration will occur to 25.6% of patients in 10 years (Hilibrand A S, Carlson G D, Palumbo M A, et al. Radiculopathy and myelopathy at segments adjacent to the site of a previous anterior cervical arthrodesis [J]. J Bone Joint Surg Am, 1999, 81 (4): 519-528.). The biomechanical experimental results also confirmed that pressure inside the intervertebral disc of the adjacent segments is increased after the fusion surgery. Kinematic iconography evidence also illustrated that relative movability of adjacent segment vertebras is increased after the fusion surgery. The above factors are very likely to accelerate the postoperative adjacent segment degeneration.
For overcoming the loss of movability of the operated segment, adjacent segment degeneration and other shortcomings, scientists and doctors in the world have established a non-fusion vertebral surgery method whose philosophy is motion preservation. The artificial intervertebral disc replacement surgery (also known as intervertebral disc arthroplasty) is a typical non-fusion surgery. Intervertebral disc prostheses such as Bryan prosthesis, ProDisc-C prosthesis, Prestige prosthesis and PCM prosthesis are mainly utilized for clinical application. Currently, best indications for artificial disc replacement surgery are single segment and physiological cervical curvature (Sekhon L H. Cervical arthroplasty in the management of spondylotic myelopathy [J]. J SpinalDisord Tech, 2003, 16 (4): 307-313). Recognized contraindications are osteoporosis and intervertebral instability (Wiffield C C, Skrzyp iec D, Jackowski A, et al. Internal stress distribution in cervical intervertebral discs: the influence of an artificial cervical joint and simulated anterior interbody fusion [J ]. J Spinal Disord Tech, 2003, 16 (5): 441-449.). Although artificial intervertebral discs have different materials and shapes, the common disadvantages are as follows: first, only single replacement of intervertebral disc is able to be provided and the combined vertebral lesions (such as vertebral tumors and surgeries needing vertebral decompression) cannot be treated. Second, most scholars do not agree to multi-segment intervertebral disc replacement, especially the replacement of adjacent intervertebral discs at the same time.
In summary, the conventional technology is not able to solve the problem of movability after cervical vertebra surgery, especially the problem of no movability after multi-segment surgery and the adjacent segment degeneration after fusion surgery.
Accordingly, an adjustable complex of an artificial cervical vertebra and an intervertebral connector with support function like the artificial vertebra and movability like the artificial intervertebral disc is developed according to the present invention.